Airbag made from low tenacity yarns

ABSTRACT

An airbag cushion having a novel seam structure including either a tri-stitch fold-over seam structure or a double-stitch fold-over seam structure. The novel seam structure allows airbag cushions to be manufactured by using low tenacity yarns, preferably in the range of between about 40 cN/tex and about 65 cN/tex.

BACKGROUND OF THE INVENTION

Airbag systems function by employing a sensor to detect a collisionevent, which triggers an inflator component to inflate the airbagcushion at high pressure. As a result of this process, the airbagcushion is subjected to a sudden and violent increase in gas pressure,which is then compounded by the impact of a vehicle occupant exertingexternal pressure against the airbag cushion. In order for the airbagcushion to protect occupants in a vehicle, it is necessary for theairbag to exhibit high burst strength.

Heretofore, various attempts have been made to manufacture an airbagcushion that is strong, robust, and exhibits high burst strength. Onegenerally accepted method for manufacturing such cushions is byutilizing high tenacity multifilament yarns having tenacity of greaterthan 8.0 grams/denier (g/den).

Japanese unexamined patent publication no. 4-5,145 teaches anon-circular airbag made from hollow weave fabrics having an axis lengththereof in a direction at a bias angle of 45 degrees from the warpdirection, corresponding to 70 to 95% of the axis length thereof in thewarp and weft direction.

Japanese unexamined patent publication no. 4-43,143 discloses an airbagmade from non-circular hollow weave fabric pieces having a longer axisin a direction inclined at a bias angel from the warp or weft directionthan an axis in the warp direction of the fabric pieces.

These attempts are based on the idea that a starting point in burstingof the airbag cushion resides in a seam-joining portion in acircumferential edge portion of the cushion, and provided a cushion madefrom non-circular woven fabric pieces having shorter axis in a biasdirection than that in the warp or weft direction, to enhance the burststrength of the seam-joining portion.

U.S. Pat. No. 5,470,106 discloses the use of a woven fabric apron at thearea surrounding the inflator connection to improve burst strength.Other attempts to improve burst strength have included the use ofadhesive means to reinforce the weaker areas of the airbag. U.S. Pat.No. 5,296,278 teaches that bags having yarns with tensile strengthmeasurements of less than 8.0 g/den (approximately 70 cN/tex or centiNewton/tex) do not perform well. This reference also discloses a meansfor applying silicone rubber at the seams to prevent fraying of thecoated fabric to prevent failure at the seams.

Most of the efforts to improve the burst strength of airbag cushionshave been focused on using high tenacity yarns, occasionally incombination with some other means or method for increasing seamstrength. However, none of the prior art has provided an airbag cushionhaving a novel seam and low tenacity yarns in combination to providehigh burst strength. One advantage to using low tenacity yarns in airbagcushion applications is that low tenacity yarns generally may bemanufactured or purchased at a lower cost than high tenacity yarns.

OBJECTS OF THE INVENTION

Accordingly, it is an object of the present invention to provide anairbag cushion employing yarns having tenacity of less than 70 cN/texwhile maintaining high burst strength.

Another object of the present invention is to provide an airbag cushionhaving a novel seam construction that allows an airbag cushion to bemanufactured using low tenacity yarns without sacrificing acceptablelevels of burst strength.

Still another object of the present invention is to provide a method formanufacturing an airbag cushion using yarns having tenacity of less than70 cN/tex while maintaining high burst strength.

Yet another object of the present invention is to provide an airbagcushion that is inexpensive to manufacture, and which overcomes some ofthe problems commonly associated with other airbag cushions.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1A is a side view of a traditional seam structure utilized onairbag cushions;

FIG. 1B is a cross-sectional view of the traditional seam structureshown in FIG. 1A;

FIG. 1C is a magnified cross-sectional view of the traditional seamstructure shown in FIG. 1B;

FIG. 2A is a side view of an airbag cushion having a novel tri-stitchfold-over seam structure;

FIG. 2B is a cross-sectional view illustrating the novel tri-stitchfold-over seam structure shown in FIG. 2A;

FIG. 2C is a magnified cross-sectional view of the novel tri-stitchfold-over seam structure shown in FIG. 2B;

FIG. 3A is a side view of an alternate embodiment of the airbag cushionshown in FIGS. 2A-2C, where the seam direction is reversed;

FIG. 3B is a cross-sectional view illustrating the novel tri-stitchfold-over seam structure in the reverse direction;

FIG. 3C is a magnified cross-sectional view illustrating the noveltri-stitch fold-over seam structure in the reverse direction;

FIG. 4A is a side view of another embodiment of an airbag cushion havinga novel tri-stitch fold-over seam, where the folded over portion of theseam is on the inner portion of the bag;

FIG. 4B is a cross-sectional view illustrating the novel tri-stitchfold-over seam shown in FIG. 4A;

FIG. 4C is a magnified cross-sectional view illustrating the noveltri-stitch fold-over seam structure shown in FIG. 4B;

FIG. 5A is a side view of another embodiment of an airbag cushion havinga novel double-stitch fold-over seam;

FIG. 5B is a magnified cross-sectional view illustrating the noveldouble-stitch fold-over seam shown in FIG. 5A;

FIG. 5C is a magnified cross-sectional view illustrating the noveldouble stitch fold-over seam structure shown in FIG. 5B.

DESCRIPTION

Airbag cushions typically comprise at least two fabric panels, eachhaving a desired shape, sewn together to form a three-dimensionalstructure. FIGS. 1A-1C show a traditional double needle chain stitchseam structure 10 that has been commonly employed as a means for joiningtogether fabric blanks that form airbag cushions. A first fabric blank12 is joined to a second fabric blank 14 by means of an inner stitch 16and an outer stitch 18. The double needle chain stitch structure hasbeen used in the past because a single stitch did not provide enoughseam strength, and the burst strength of a bag employing such a seamstructure suffered from unacceptably low burst strength.

One problem associated with the double needle chain stitch seamstructure is that the high pressure caused by an airbag inflator causesthe seam to tend toward peeling open (a condition referred to herein asthe peel mode). FIG. 1C shows the double needle chain stitch seamstructure under stress in the peel mode. When the cushion expands due tothe inflation pressure, the inner stitch receives the maximum stress,which sometimes results in the needle penetration holes formed by theinner stitch becoming susceptible to heat erosion from the got inflationgases. The strength of the seams during the peel mode equals only about60% to 70% of the strength of the fabric.

In order to improve the seam strength of the double needle chain stitchseam structure, thus increasing the burst strength of the airbagcushion, a third stitch 20 was added to the seam structure as shown inFIGS. 2A-2C. The third stitch 20 joins the first and second fabricblanks together, similarly to the inner stitch 16 and the outer stitch18, but also joins the first fabric blank back onto itself in a foldedmanner as shown. Such an arrangement converts the stress condition onthe seam structure from a peel mode to a shear mode, which spreads thestress load over multiple stitches within the seam, rather than having asingle stitch bear the entire stress load. This seam arrangement,referred to herein as a tri-stitch fold-over seam (or tri-stitch),provides 100% of the fabric strength at the seams, and protects theinner 16 and outer stitches 18 against hot gas erosion. Thus, the onlypossible gas leak area, between the inner 16 and outer stitches 18, iscovered by a double layer of fabric.

Alternate embodiments are shown in FIGS. 3A-3C, where the second fabricpanel is folded over onto itself, rather than the first fabric panelbeing folded over, as shown in FIGS. 2A-2C. FIGS. 4A-4C illustrateanother alternate embodiment of the tri-stitch fold-over seam structure,where the second fabric panel is folded over onto itself, and where thefolded portion is on the inside of the cushion rather than the outsideof the airbag cushion. FIGS. 5A-5C illustrate an alternate embodiment ofthe novel seam structure, which is a double-stitch fold-over seam. Inthis embodiment, instead of applying two parallel seams to attach thefabric blanks prior to the fold-over step, the fabric blanks areattached using a single seam, and then the fabric seam is folded overand connected using a fold-over seam, as shown.

Using the tri-stitch fold-over seam or the double-stitch fold-over seamas described above allows airbag cushions to be manufactured with lowtenacity yarns, where the use of such low tenacity yarns has not beenpossible in prior airbag cushion applications. Because the tri-stitchand double-stitch fold-over seams (collectively called “shear seams”herein) significantly strengthens the seam of the cushion, the necessityof using of high tenacity yarns in order to maintain acceptable burststrength levels for airbag cushions is obviated.

One preferred yarn is polyester. The preferred tenacity range is betweenabout 60 cN/tex and about 35 cN/tex. A second preferred range is about50 cN/tex and about 40 cN/tex. The most preferred range is about 55cN/tex and about 45 cN/tex. Although a specific yarn type has beendisclosed, it is to be understood that any suitable yarn may be used.

The effectiveness of the seam as related to burst strength isillustrated in the following examples:

EXAMPLE 1 Comparison of Low Tenacity vs. High Tenacity using TraditionalStitch

A multifilament 620d polyester yarn of tenacity 5.1 g/den (45 cN/tex)was woven in the water-jet loom in a plain weave with a construction of40×40 yarns per inch. This fabric was then calendared to achieve surfacesmoothness and coated with silicone rubber at a weight of 0.74 oz/sq.yd. A comparison of physical properties of this low tenacity fabric isshown in the following table along with a typical 630d nylon 6,6silicone coated airbag fabric.

TABLE 1 Physical Properties of Airbag Fabrics 630d NY 6,6 620d PET-LowAirbag Fabric Tenacity Fabric Yam Tenacity g/den.  9.3  5.1 Fabricconstruction, Per inch  41/40  40/40 W/F Fabric total weight Oz/sq. yd. 8.06  6.89 Coating Add-on Oz/sq. yd.  1.1  0.74 Grab Tensile, W/F Lbs/inch 611/585 487/499 Elongation, W/F %  35.1/37.1  38.4/35.2 TongueTear, W/F Lbs.  50/55  42.5/53 Flammability In/min No Burn Rate No BurnRate King Stiffness Lbs  2.4  1.9 Fabric Modulus Lbs/inch 960 720

Tethered driver airbags of 52L volume was made from both of the abovefabrics using the typical seaming techniques as shown in FIG. 1. Twocircular shaped panels were sewn along the perimeter with a doubleneedle chain stitch. After the bags are turned inside out as shown, theperimeter seams are in the peel mode.

Airbag cushions manufactured using the above fabrics (one cushion madefrom high tenacity yarns, and one made from low tenacity yarns)employing traditional double needle chain stitch sewing techniques weretested with a 220-kPa-driver inflator statically and under loading.Nylon 6,6 bags performed well as expected, but the low tenacitypolyester bags exhibited heat erosion at the perimeter seams resultingin considerable loss of pressure. Effective restraint functionality waslost in the low tenacity polyester bags because of the steep pressuredecay (<1.0 Psi at 45 msec). Even though the polyester fabric wascoated, the uncoated side of the yarns gets exposed very easily to heatbecause of higher elongation at the seams with the low tenacity yarns.Also, with the heat capacity of Polyester being 1.5 kJ/kg. K compared to1.7 kJ/kg. K for nylon, it is desirable to protect the uncoated side ofthe yarn at the seams and improve the seam overall.

EXAMPLE 2 Cushion Performance (High Tenacity vs. Low Tenacity) usingTri-Stitch

The tri-stitch fold-over seam modification was implemented on sets of52L driver bags made from silicone coated fabric woven with the lowtenacity polyester yarns and high tenacity Nylon 6,6 yarns,respectively. As before, these bags were tested statically and underload with the same 220 kPa driver inflator as before. Test results aresummarized in the following Table 2.

TABLE 2 Bag Performance Parameters Average Peak Bag BAG TYPE Pressure(Psi) 630d NY 6,6 with tri-stitch fold-over seam 10.85 (Shear seam) 630dNY 6,6 traditional seam (Peel seam) 9.5 620d PET with tri-stitchfold-over seam 11.9 (Shear seam) 620d PET traditional seam (Peel seam)<1.0

Restraint functionality in terms of energy absorption for the new bagwith low tenacity yarns was equivalent or better than traditionalairbags made from high tenacity yarns. Visual inspection of the bags didnot reveal any sign of heat erosion at the seams

EXAMPLE 3 Drop Tests

A set of airbag cushions were manufactured using 630d Nylon 6,6 at aconstruction of 41×41 yarns per inch for the control group, and fabricthat was woven with low tenacity (4.8 g/den) polyester yarn of 620d at aconstruction of 40×40 yarns per inch was used to manufacture a secondset of airbag cushions. Both the fabrics were woven on the waterjet loomand were silicone coated at a coating weight of 0.7 oz./sq. yd. All ofthe polyester cushions had the tri-stitch fold-over seam construction asshown in FIG. 3. The inflator used for these tests was a 231 kPainflator (in 60L tank test) which is considered to be an aggressiveinflator in the airbag industry.

Drop tests were conducted on the airbags by dropping a weight of 75 lbs.from a height of 6 feet onto the inflated bag. The 12 inch×24 inchsurface of the weight facing the bag was in the horizontal plane and theweight was constrained so it could move only up or down in the verticaldirection. The peak deceleration rate as well as the peak-rebound heightof the weight was recorded.

TABLE 3 Drop Test with Inflator (average of 6 bags each) Bag ReboundCompression Pressure Distance Distance (Psi) Peak G's (in) (in) 630dNylon 6,6 10.2 20.8 27.5 5.84 Airbag - traditional seam 620d LowTenacity 11.4 16 <10 5.43 PET Airbag - tri stitch fold-over seam

The peak deceleration experienced by an object being brought to rest byan airbag is an important parameter in determining airbag performance.The peak deceleration measured in G's (multiples of the standardacceleration due to gravity) multiplied by the body weight gives theforce exerted on the body to bring it to rest. Another importantparameter is the amount of rebound experienced by an object after it isbrought to rest. This parameter is a measure of energy imparted to theobject by the airbag after bringing the object to rest and plays a rolein possible secondary injury such as whiplash.

Although the present invention has been described in considerable detailwith reference to certain preferred versions thereof, other versions arepossible. Therefore, the spirit and scope of the appended claims shouldnot be limited to the description of the preferred versions containedherein.

1. An airbag cushion comprising: at least one fabric blank includingmultifilament yarns having a tenacity of no greater than about 40cN/tex, wherein said blank has an elongation in each of the warp andfilling directions of less than 40%.
 2. The airbag cushion set forth inclaim 1, wherein said multifilament yarns comprise polyester continuousfilament yarn.
 3. The airbag cushion set forth in claim 2 wherein saidpolyester continuous filament yarns are in the range of about 100 toabout 800 denier continuous filament yarns.
 4. The airbag cushion setforth in claim 2, wherein said polyester continuous filament yarnscomprise a plurality of filaments having a linear density in the rangeof about 2 to about 6 denier per filament.
 5. The airbag cushion setforth in claim 2, wherein said polyester continuous filament yarnscomprise a plurality of filaments having a linear density in the rangeof about 4 to about 6 denier per filament.
 6. The airbag cushion setforth in claim 1, wherein said airbag cushion further comprises acoating applied to at least one surface thereof.
 7. The airbag cushionset forth in claim 6, wherein said coating comprises at least 70%silicone resin in an amount of about 0.5 to 2.0 oz/sq. yd.
 8. An airbagcushion comprising: at least one fabric blank including multifilamentyarns having a tenacity of no greater than about 55 cN/tex, wherein saidblank has an elongation in each of the warp and filling directions ofless than 40%, said airbag cushion further comprising at least onetri-stitch fold-over seam structure.
 9. An airbag cushion comprising: atleast one fabric blank including multifilament yarns having a tenacityof no greater than about 55 cN/tex, wherein said blank has an elongationin each of the warp and filling directions of less than 40%, said airbagcushion further comprising at least one double-stitch fold-over seam.10. The airbag cushion of claim 9 wherein said multifilament yarns areabout 150 denier continuous filament yarns or multiples of about 150denier continuous filament yarns and wherein said multifilament yarnscomprise a plurality of filaments having a linear density in the rangeof about 2 to about 6 denier per filament.
 11. The airbag cushion setforth in claim 9, further comprising a coating applied to at least onesurface of the fabric, wherein said coating amount is about 0.2 oz/sq ydto about 2.0 oz/sq yd.
 12. An airbag cushion having a tri-stitchfold-over seam, said cushion having at least one fabric blank includingmultifilament yarns with a tenacity of no greater than about 60 cN/tex.13. An airbag cushion having a double-stitch fold-over seam, saidcushion having at least one fabric blank including multifilament yarnswith a tenacity of no greater than about 60 cN/tex.
 14. The airbagcushion according to claim 12, wherein said cushion comprises at leastone fabric blank including multifilament yarns having a tenacity of nogreater than about 55 cN/tex.
 15. The airbag cushion according to claim13, wherein said cushion comprises at least one fabric blank includingmultifilament yarns having a tenacity of no greater than about 55cN/tex.
 16. An airbag cushion comprising: (a) at least one fabric blank,said fabric blank having multifilament yarns with a tenacity of nogreater than about 40 cN/tex, and (b) further wherein said fabric blankhas an elongation in each of the warp and filling directions of lessthan 40%.
 17. The airbag cushion of claim 16 wherein said cushionfurther includes a coating on at least one surface of said airbagcushion.
 18. The airbag cushion of claim 17 wherein said coatingcomprises at least 70% silicone resin in en amount of about 0.5 to about2.0 oz/square yard.